a. Field of the Invention
The present invention relates to a three-step switch and, more particularly, to a three-step press switch, which achieves a three-step switching operation when continuously pressed at different times.
b. Description of the Prior Art
A variety of electric switches including sliding switches, rotary switches, press switches, and etc., have been disclosed for use with electric apparatus. Regular electric switches are commonly of two-step type adapted to switch on/off the power circuit of an electric apparatus. For an electric apparatus having two power circuits, two switches must be used. However, the use of multiple switches greatly increases the cost of the electric apparatus, and requires much installation space. Taiwan Patent publication no. 275966 discloses an improved structure of three-step switch, which, as shown in FIG. 1, is a sliding switch comprised of a housing 11, a slide 12 mounted in the housing 11, and a movable metal contact plate 13 moved with the slide 12 to one of three positions, namely, the first position where the movable metal contact plate 13 contacts the first fixed metal contact plate A to close the first circuit, a second position where the movable metal contact plate 13 is disconnected from the first fixed metal contact plate A and the second fixed metal contact plate B to open the first circuit and the second circuit, and a third position where the movable metal contact plate 13 contacts the second fixed metal contact plate B to close the second circuit. Taiwan patent no. 409932 discloses a three-step lamp switch, which, as shown in FIG. 2, is a rotary switch comprised of a housing 14, a rotary knob 15, and a metal contact plate 16 rotated with the rotary knob 15 to alternatively touch the first fixed metal contact plate 17 or the second fixed metal contact plate (not shown), or not to touch the first fixed metal contact plate and the second fixed metal contact plate. According to the aforesaid two three-step switch designs, the slide 12 or the rotary knob 15 are exposed to the outside of the housing 11 or 14 for operation by hand. However, these two designs cannot be covered with waterproof cover means to protect against outside water. When adding waterproof cover means to housing, the waterproof cover means may hinder the movement of the slide or rotary knob.
Further, regular two-step press switch, for example, the press-button switch of an automatic pen can be covered with a waterproof covering to protect the internal circuit against outside water. However, this design of press switch can be switched between two positions(ON less than - greater than OFF) only, its application is limited.
The present invention has been accomplished under the circumstances in view. It is the main object of the present invention to provide a three-step switch, which achieves three-step switching operation by pressing. It is another object of the present invention to provide a three-step press switch, which is inexpensive to manufacture. It is still another object of the present invention to provide a three-step press switch, which requires less installation space. It is still another object of the present invention to provide a three-step switch, which is suitable for use in a waterproof product. To achieve these and other objects of the present invention, the three-step press switch is comprised of a casing shaped like a stepped tube, said casing comprising a first receiving chamber and a second receiving chamber, said first receiving chamber comprising a plurality of longitudinal guide grooves equiangularly spaced around an inside wall thereof, said longitudinal guide grooves each having a beveled bottom side, an outer thread around the periphery of an upper part thereof, and a flange extended around the periphery of a middle part thereof; an actuating device mounted in the first receiving chamber of the casing and forced to rotate through an angle when pressed, the actuating device comprised of a press member, a rotary member, and a spring, the press member being a hollow, bottom-open shell, comprising a plurality of longitudinal ribs spaced around the periphery of a lower part thereof and respectively coupled to the longitudinal guide grooves of the casing to guide vertical movement of the press member in the casing and a downwardly extended serrated bottom edge, the rotary member being a hollow, bottom-open shell, comprising a top insertion portion inserted into the press member from a bottom side, an upwardly extended serrated portion disposed around the periphery thereof on the middle and meshed with the serrated bottom edge of the press member, the spring of the actuating device being mounted in the rotary member to impart an upward pressure to the rotary member and the press member; wherein the second receiving chamber of the casing comprises a plurality of three openings in the periphery thereof, three downward pins respectively suspending in the openings, a first metal contact plate coupled to one of the downward pins and disposed at one side of the casing, a second metal contact plate and a third metal contact plates disposed at one side of the casing opposite to the first metal contact plate and arranged at right angles; the rotary member comprises two downwardly extended driving rods adapted to rotate a metal conducting member below; the three-step press switch further comprises a bottom cover covered on a bottom side of the casing, a second spring mounted in the bottom cover, and a metal conducting member supported on the second spring and coupled to the rotary member for synchronous rotation with the rotary member relative to one of a series of positions including a first position where the first metal contact plate and the second metal contact plate and the third metal contact plate are electrically disconnected, a second position where the metal conducting plate is disposed in contact with the first metal contact plate and the second metal contact plate to electrically connect the first metal contact plate and the second metal contact plate, and a third position where the metal conducting plate is disposed in contact with the first metal contact plate and the third metal contact plate to electrically connect the first metal contact plate and the third metal contact plate, the metal conducting plate comprising a flat base supported on the second spring and an upright rod upwardly extended from the center of the flat base and inserted into the rotary member from a bottom side, the flat base comprising two peripheral lugs disposed at two sides and adapted to contact the first metal contact plate, the second metal contact plate and the third metal contact plate, and two peripheral notches respectively coupled to the downwardly extended driving rods of the rotary member for enabling the metal conducting member to be rotated with the rotary member when the press member is pressed by an external force.